85 research outputs found
Exploiting Multi-Antennas for Opportunistic Spectrum Sharing in Cognitive Radio Networks
In cognitive radio (CR) networks, there are scenarios where the secondary
(lower priority) users intend to communicate with each other by
opportunistically utilizing the transmit spectrum originally allocated to the
existing primary (higher priority) users. For such a scenario, a secondary user
usually has to trade off between two conflicting goals at the same time: one is
to maximize its own transmit throughput; and the other is to minimize the
amount of interference it produces at each primary receiver. In this paper, we
study this fundamental tradeoff from an information-theoretic perspective by
characterizing the secondary user's channel capacity under both its own
transmit-power constraint as well as a set of interference-power constraints
each imposed at one of the primary receivers. In particular, this paper
exploits multi-antennas at the secondary transmitter to effectively balance
between spatial multiplexing for the secondary transmission and interference
avoidance at the primary receivers. Convex optimization techniques are used to
design algorithms for the optimal secondary transmit spatial spectrum that
achieves the capacity of the secondary transmission. Suboptimal solutions for
ease of implementation are also presented and their performances are compared
with the optimal solution. Furthermore, algorithms developed for the
single-channel transmission are also extended to the case of multi-channel
transmission whereby the secondary user is able to achieve opportunistic
spectrum sharing via transmit adaptations not only in space, but in time and
frequency domains as well.Comment: Extension of IEEE PIMRC 2007. 35 pages, 6 figures. Submitted to IEEE
Journal of Special Topics in Signal Processing, special issue on Signal
Processing and Networking for Dynamic Spectrum Acces
Interference Mitigation for Cognitive Radio MIMO Systems Based on Practical Precoding
In this paper, we propose two subspace-projection-based precoding schemes,
namely, full-projection (FP)- and partial-projection (PP)-based precoding, for
a cognitive radio multiple-input multiple-output (CR-MIMO) network to mitigate
its interference to a primary time-division-duplexing (TDD) system. The
proposed precoding schemes are capable of estimating interference channels
between CR and primary networks, and incorporating the interference from the
primary to the CR system into CR precoding via a novel sensing approach. Then,
the CR performance and resulting interference of the proposed precoding schemes
are analyzed and evaluated. By fully projecting the CR transmission onto a null
space of the interference channels, the FP-based precoding scheme can
effectively avoid interfering the primary system with boosted CR throughput.
While, the PP-based scheme is able to further improve the CR throughput by
partially projecting its transmission onto the null space.Comment: 12 pages, 4 figures, submitted to the IEEE Trans. Wireless
Communications in April 201
Cooperative underlay cognitive radio assisted NOMA: secondary network improvement and outage performance
In this paper, a downlink scenario of a non-orthogonal multiple access (NOMA) scheme with power constraint via spectrum sensing is considered. Such network provides improved outage performance and new scheme of NOMA-based cognitive radio (CR-NOMA) network are introduced. The different power allocation factors are examined subject to performance gap among these secondary NOMA users. To evaluate system performance, the exact outage probability expressions of secondary users are derived. Finally, the dissimilar performance problem in term of secondary users is illustrated via simulation, in which a power allocation scheme and the threshold rates are considered as main impacts of varying system performance. The simulation results show that the performance of CR-NOMA network can be improved significantly
Interference-Aware Resource Control in Multi-Antenna Cognitive Ad Hoc Networks with Heterogeneous Delay Constraints
In this work, we consider a multi-antenna cognitive ad hoc network (CAHNet)
with heterogeneous delay requirements. To fulfill the interference and delay
constraints simultaneously, we propose to perform adaptive zero-forcing
beamforming (ZFBF) at cognitive transmitters according to interference channel
state information (CSI). To assist the CAHNet to obtain the interference CSI,
we use a win-win inter-network cooperation strategy, namely quantized
interference CSI feedback from the primary network to CAHNet through a feedback
link, under the condition that the CAHNet pays a proper price for it.
Considering the scarcity of feedback and power resources, we focus on the
minimization of the overall resource cost subject to both interference and
delay constraints. To solve the problem, we derive a joint feedback and power
control algorithm amongst multiple links of CAHNet. Finally, simulation results
validate the effectiveness of the proposed algorithm.Comment: 4 pages, 2 figure
Low-Cost Hybrid Analog-Digital Beamformer Evaluation in Spectrum Sharing Systems
This paper evaluates different analog-digital beamforming solutions for future spectrum sharing mm-wave scenarios.
In contrast to sub-6 GHz multiantenna schemes where all-digital solutions provide an excellent performance-cost tradeoff,
in the mm-wave bands where a very large number of antennas is required, all-digital designs cannot be deployed due to their cost and complexity. In order to solve this problem, subarray solutions are conceived such that a reduced number of radiofrequency chains are simultaneously connected to different antennas through an analog beamforming network formed by phase shifters (i.e. with no amplitude control). Different connectivity solutions are evaluated; namely, full-connected, localized and interleaved considering that either the phase shifters have full resolution or only one control bit. As reported in the paper, while for the full resolution case the same performance is obtained for all connectivity schemes, in case the phase shifters have one control bit, differences show up. The numerical evaluation is done with an alternating feasible point pursuit successive convex approximation (FPP-SCA) optimization which yields to efficient solutions even for this non-convex optimization problem
Cooperative Cognitive Relaying Under Primary and Secondary Quality of Service Satisfaction
This paper proposes a new cooperative protocol which involves cooperation
between primary and secondary users. We consider a cognitive setting with one
primary user and multiple secondary users. The time resource is partitioned
into discrete time slots. Each time slot, a secondary user is scheduled for
transmission according to time division multiple access, and the remainder of
the secondary users, which we refer to as secondary relays, attempt to decode
the primary packet. Afterwards, the secondary relays employ cooperative
beamforming to forward the primary packet and to provide protection to the
secondary destination of the secondary source scheduled for transmission from
interference. We characterize the diversity-multiplexing tradeoff of the
primary source under the proposed protocol. We consider certain quality of
service for each user specified by its required throughput. The optimization
problem is stated under such condition. It is shown that the optimization
problem is linear and can be readily solved. We show that the sum of the
secondary required throughputs must be less than or equal to the probability of
correct packets reception.Comment: This paper was accepted in PIMRC 201
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